Cohen Lawrence B.

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Cohen
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Lawrence B.
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Author: Homma, Ryota ×

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  • Article
    Sparsened neuronal activity in an optogenetically activated olfactory glomerulus
    (Nature Publishing Group, 2018-10-08) Braubach, Oliver R. ; Tombaz, Tuce ; Geiller, Tristan ; Homma, Ryota ; Bozza, Thomas ; Cohen, Lawrence B. ; Choi, Yunsook
    Glomeruli are the functional units of olfactory information processing but little remains known about their individual unit function. This is due to their widespread activation by odor stimuli. We expressed channelrhodopsin-2 in a single olfactory sensory neuron type, and used laser stimulation and simultaneous in vivo calcium imaging to study the responses of a single glomerulus to optogenetic stimulation. Calcium signals in the neuropil of this glomerulus were representative of the sensory input and nearly identical if evoked by intensity-matched odor and laser stimuli. However, significantly fewer glomerular layer interneurons and olfactory bulb output neurons (mitral cells) responded to optogenetic versus odor stimuli, resulting in a small and spatially compact optogenetic glomerular unit response. Temporal features of laser stimuli were represented with high fidelity in the neuropil of the glomerulus and the mitral cells, but not in interneurons. Increases in laser stimulus intensity were encoded by larger signal amplitudes in all compartments of the glomerulus, and by the recruitment of additional interneurons and mitral cells. No spatial expansion of the glomerular unit response was observed in response to stronger input stimuli. Our data are among the first descriptions of input-output transformations in a selectively activated olfactory glomerulus.
  • Preprint
    Perceptual stability during dramatic changes in olfactory bulb activation maps and dramatic declines in activation amplitudes
    ( 2007-03-30) Homma, Ryota ; Cohen, Lawrence B. ; Kosmidis, E. K. ; Youngentob, S. L.
    We measured the concentration dependence of the ability of rats to identify odorants and compared these results with the calcium signals in the nerve terminals of the olfactory receptor neurons. Odorant identification remained far above random chance at all concentrations tested (between 0.0006% and 35% of saturated vapor). In contrast the calcium signals were much smaller than their maximum values at odorant concentrations less than 1% of saturated vapor. Extrapolation suggests that only a few spikes in olfactory sensory neurons may be sufficient for correct odorant identification.
  • Preprint
    Optical analysis of circuitry for respiratory rhythm in isolated brainstem of foetal mice
    ( 2008-09) Muller, Kenneth J. ; Tsechpenakis, Gavriil ; Homma, Ryota ; Nicholls, John G. ; Cohen, Lawrence B. ; Eugenin, Jaime
    Respiratory rhythms arise from neurons situated in the ventral medulla. We are investigating their spatial and functional relationships optically by measuring changes in intracellular calcium using the fluorescent, calcium-sensitive dye Oregon Green 488 BAPTA-1 AM while simultaneously recording the regular firing of motoneurons in the phrenic nerve in isolated brainstem/spinal cord preparations of E17 to E19 mice. Responses of identified cells are associated breath by breath with inspiratory and expiratory phases of respiration and depend on CO2 and pH levels. Optical methods including two-photon microscopy are being developed together with computational analyses. Analysis of the spatial pattern of neuronal activity associated with respiratory rhythm, including cross-correlation analysis, reveals a network distributed in the ventral medulla with intermingling of neurons that are active during separate phases of the rhythm. Our experiments, aimed at testing whether initiation of the respiratory rhythm depends on pacemaker neurons, on networks or a combination of both, suggest an important role for networks.
  • Article
    In vivo functional properties of juxtaglomerular neurons in the mouse olfactory bulb
    (Frontiers Media S.A., 2013-02-21) Homma, Ryota ; Kovalchuk, Yuri ; Konnerth, A. ; Cohen, Lawrence B. ; Garaschuk, Olga
    Juxtaglomerular neurons represent one of the largest cellular populations in the mammalian olfactory bulb yet their role for signal processing remains unclear. We used two-photon imaging and electrophysiological recordings to clarify the in vivo properties of these cells and their functional organization in the juxtaglomerular space. Juxtaglomerular neurons coded for many perceptual characteristics of the olfactory stimulus such as (1) identity of the odorant, (2) odorant concentration, (3) odorant onset, and (4) offset. The odor-responsive neurons clustered within a narrow area surrounding the glomerulus with the same odorant specificity, with ~80% of responding cells located ≤20 μm from the glomerular border. This stereotypic spatial pattern of activated cells persisted at different odorant concentrations and was found for neurons both activated and inhibited by the odorant. Our data identify a principal glomerulus with a narrow shell of juxtaglomerular neurons as a basic odor coding unit in the glomerular layer and underline the important role of intraglomerular circuitry.